Half-tone printing plate



Oct. 5, 1965 s. w. LEVINE HALF-TONE PRINTING PLATE Original Filed Dec.23, 1959 M Q 9 R m wwk m am 4 8 9 5 9 5 ll M/ 8 W 1 5 E R mm mmm M. m wR A M M 2 B A H 7 M 5 y 0 B a mi A 4 ACW w s a 4 Lf M- I W Ill w J FD mm6 6 MM SAMUEL W. LEV/N INVENTOR.

3am? K JJOUBLE- FREQ. p075 United States Patent 3,209,687 HALF-TONEPRINTING PLATE Samuel W. Levine, Westhury, N.Y., assignor to FairchildCamera and Instrument Corporation, a corporation of Delaware Originalapplication Dec. 23, 1959, Ser. No. 861,625, now Patent No. 3,075,042,dated Jan. 22, 1963. Divided and this application Apr. 26, 1962, Ser.No. 195,359 3 Claims. (Cl. 101-401) This is a division of applicationS.N. 861,625, filed Dec. 23, 1959, and now US. Patent 3,075,042, issuedJan. 22, 1963.

This invention is concerned with improvements in electronic half-toneengraving, and has for its principal object the provision of anapparatus and method, by which half-tone engraved plates of goodprinting and matting quality can be produced by the cold engraving ofplate material in a manner generally analogous to the production ofsimilar plates by the hot burning of plastic plate material. Theinvention thus provides for the provision of metal engravings, forexample on magnesium or magnesium-alloy plate stock, by the electronicline scan and point-to-point engraving procedure currently in wide useby newspapers and other printing plants.

The known apparatus and techniques referred to above are bestexemplified by the disclosure of US. Reissued Letters Patent 23,914 ofDecember '21, 1954, to J. A. Boyajean, lr., owned by the assignee of thepresent invention, utilizing the heated plate-decomposing tool thereindescribed as the preferred plate-deforming tool, and operating upon athin plate composed for example of a heatdecomposable material such ascellulose nitrate. Preferred forms of the latter material are disclosedin US. Patent No. 2,827,726, G. F. Stradar, also owned by the presentassignee.

At the present time, there are three principal types of machines for thecold engraving of half-tone printing plates direct from electricalsignals. In the first type (exemplified by the Klischograph machine ofDr. Rudolph Hell), a fiat-bed machine uses alinear scan motion toproduce a screened reproduction quite similar in structure to thedesired conventional pattern, but it is necessary to rotate the copy andthe plate at a 45 degree angle to the direction of scan, which can onlybe done by scanning a diagonal of the copy, rather than lines parallelto the rectangular copy edges. The size of copy (and plate) which agiven machine can handle is therefore considerably reduced. In a secondtype (exemplified by the Elgrama machine of Swiss origin), ahill-and-dale type of engraving is utilized resulting in a line pattern;while theoretically this machine can scan and engrave in the directionsparallel to copy edges, operators find it necessary, as a practicalmatter, to resort to 45 degree rotation of the copy and plate tominimize the line characteristic of the screen, and to reduce theproblem of ink flow which reduces detail in the shadow areas of theplate. In a third type of machine (which has been demonstratedexperimentally by Hassing), a triangular shaped dot is engraved, tocircumvent the requirement for rotating the copy. The screen so producedis not conventional, in that the dots are aligned at a 60 degree angleinstead of the usual 45 degrees characteristic of the standard screen;the dot shape also raises other problems.

In the engraving technique to be described herein, a somewhatunconventional dot structure is obtained, but one whose diiferences fromthe standard are visible only on microscopic examination. When a printedproof from the plate is examined visually, it appears to be entirelyconventional. The copy and plate can be oriented (as on a rotary typemachine) with the direction of scan paral- 3,209,687 Patented Oct. 5,1965 lel to an edge of the copy, yet the rows of dots line up at thedesired 45 degree angle. The achievement of this angular alignment isvery important, because it happens that the human eye can resolvedetails much better when the detail is aligned in either a horizontal orvertical direction, and resolves least when the details are aligned atthe 45 degree angle. If a plate is engraved with the dots alignedvertically or horizontally, they become very apparent to the eye, whichis objectionable since the entire basis for half-tone reproduction isthe suppression of the effects of the individual dots in favor of theover-all impression of continuity of tones.

It is accordingly a further object of the invention to provide ways andmeans for accomplishing the electronic half-tone cold engraving of metalor like hard plate material, to yield in a single complete scanningoperation a plate having the desired tonal range, proper dot structureand shape, and the other properties deemed requisite by those using suchplates for printing operations.

It is a further object of the invention to provide ways and means forproducing a cold engraved half-tone plate having the desired staggeringof the dots of successive rows, without the necessity for cocking or theturning of the original copy and plate material at a 45 degree anglerelative to the directions of scan; thereby making it possible toengrave plates of full size up to the normal limits of the engravingequipment employed.

Still another object of the invention is to provide an engraving systemof the above type which can be carried out with rotary plate-handlingmachines such as described in the Reissue patent referred to above, withthe copy and the plate oriented in the usual Way, yet producing thedesired diagonal or stagger pattern of dots in the finished plate. Anadditional object of the invention is to provide a system of this kindin which the deflection of the engraving tool employed is relativelysmaller than in the case of normal hot-stylus engraving as employedheretofore with hot-stylus machinery, thereby to permit either a highereffective speed of engraving, or the production of steeper walls on thecavities in the plate material which form the dot structure. The depthof engraving for a given highlight dot size is also considerably lessthan that required for the cold engraving techniques as practiced in thethree electronic engraving machines previously discussed. Yet a furtherobject of the invention is to provide such a procedure which is capableof producing a highlight dot of very minimum size as compared with priorart efforts in electronic plate engraving. Finally, it is an object ofthe invention to produce such a process and system which can be carriedout with very simple and readily performed modifications in existingline-scan engraving equipment of the rotary cylinder type, thereby topermit a variety of difierent materials to be satisfactorily employedwith such equipment.

Briefly to summarize the way in which the above and other objects of theinvention are accomplished, it may be said that the invention utilizes acold engraving tool shaped to engrave a cavity, in metal or like platematerial, which is of diamond shapethat is, a square cavity orientedwith its sides at 45 degrees to the principal scan directions. This isaccomplished by a screen tone modulation of the engraving depth ascarried out in the machine of the reissued patent mentioned heretofore.However, after the engraving of each complete line of such cavities inone direction of scan, the same tool is employed to produce either avariable-width engraved pattern or a double-frequency engraved pattern,which thus modifies the area lying between the successive rows of' dots;but the production of the variable-width modification or the doublefrequency engraving is automatically restricted to plate regions inwhich highlight tones greater than some predetermined value are to beproduced. The result is a plate pattern which in all tonal respects isfully equivalent to the more conventional pattern of staggered squaredots of varying size.

With the above outline of the invention in mind, the actual proceduresemployed, and preferred apparatus for carrying out such procedures, willbest be understood from the following detailed specification of apreferred example thereof, taken in connection with the accompanyingdrawings, in which:

FIGURE 1 is an illustration of the cavity structure (or dot structure)of a conventional electronically engraved plate, showing a variety oftonal values in the dot pattern.

FIGURE 2 is a similar illustration of the dot structure obtained by theuse of the present invention with the hilland-dale variable widthauxiliary engraving, together with an indication of the manner in whichit is obtained.

FIGURE 3 is a similar illustration of the dot structure obtained by theuse of the present invention utilizing the double frequency auxiliaryengraving line, together with an indication of the manner in which it isobtained.

FIGURE 4 is a schematic illustration, sufficient to enable those skilledin the art to practice the invention, of a preferred form of apparatusby which the invention may be accomplished.

Referring first to FIGURE 1 of the drawings, there is illustrated theform of printing plate obtained by the use of the machine of theBoyajean patent already mentioned, said plate being obtained bycontrolling from point to point the depth of entry of a hot stylus intothe material of a decomposable flexible plate indicated generally bynumeral 10. Such plates are printed by inking the printing surface, sothe surface at the left end of FIGURE 1 corresponds to a shadow tone inthe reproduction. The dot structure consists of alternately staggeredrows of square indentations or cavities 12 whose area, at the printingsurface, is a relatively small fraction of the total undisturbed areasurrounding each dot. In the central portion of FIGURE 1, a middle-tonedot structure 14 is indicated, in which the cavity area has increased toa \larger fraction, specifically to a fraction greater than one-half.This is possible because the square-topped cavities produced by thepyramidal engraving stylus point actually overlap at the printingsurface, as indicated by the dash lines at the corners. Between theareas 12 and 14, a single row of dots is shown in which the cavitiesjust touch at their corners, producing a checkerboard pattern.

The right-hand portion of FIGURE 1 illustrates a highlight tone area 16in which the excised cavities have become so large that only a smallpart of the unit area of the printing surface remains, producing amaximum highlight dot pattern. In all cases, the dots are substantiallyrectangular in outline, and arranged so that the nearest dots extend ata 45 degree angle to the vertical and horizontal edges of the originalrectangular copy and engraving material. In effect, the arrangement ofnearest dots lining up at a 45 degree angle to the horizontal andvertical makes them less easily resolved by the eye, and this is acondition that is desired.

It will be seen from the foregoing that production of such a staggereddot pattern cannot be accomplished by the engraving of continuous linesalong directions parallel to the plate edges, but that such could beattempted by performing variable-width line engraving along two sets ofmutually perpendicular lines cocked at 45 degrees to the plate edges; oralternatively by cocking the original copy (and the plate material) atsuch angle. In FIGURE 1, the scanning and engraving line direction isfrom top to bottom of the figure.

According to the invention, an acceptable cold-engraved dot patternequivalent to the known FIGURE 1 pattern can be obtained, on a singlepass of the plate material, which can be arranged at the normal anglewith its edges parallel to the scan directions, by the use of apyramidal cold engraving tool which is however angled at 45 degrees soas to engrave diamond-shaped dots such as indicated in the shadowportion 18 at the left of FIGURE 2. As the penetration depth increases,the excised diamondshaped areas become larger, as at 20, but in thiscase the signal is appropriately limited to prevent the corners of thesecavities from overlapping or touching. The middle tone area is thusrepresented by a grid of perpendicular printing-surface lines 22, theminimum width of such lines being set by the controls of the process.

Further, according to one form of the invention, the highlight area atthe right end of FIGURE 2 is obtained by removing controlled-widthfurrows of the connector grid lines 22 between each pair of theirintersection centers from top to bottom of the plate material, being thescan direction of the process. These furrows 24 (shown stippled forclarity) are produced by the same stylus which excised the cavities inthe other plate portions, the stylus having a relatively shallowincluded angle at its pyramidal point so that the width of the furrow isreadily controlled by the penetration depth, in the manner of ahill-and-dale recording of the Philips-Miller type. The result, asindicated in FIGURE 2, is a highlight dot area 26 consisting essentiallyof controlled portions of the intersections only of the waffle-patternmiddle tone area 20. It will be noted that the production of acontinuously varying furrow is readily accomplished by eliminating theon-off tone which characterizes the driving current of the stylus in thetrue dot-producing action in the shadow and middle tone regions.

In order to permit a plate as illustrated in FIGURE 2 to be produced ina single scan of the material, the variable width lines or furrows 24are preferably produced (when required by the tones value beingengraved) by the use of the engraving stylus as a continuoushill-anddale graver upon alternate passes of the sylus along the scanlines running from top to bottom of the drawing figures. In thisconnection, it will be recalled that the staggering of the dot patternsof the conventional engraving in FIGURE 1 is obtained by the use of adegree phase shift in the screen tone (or on-olf tone) during alternatelines of scan or engraving. The same procedure is used for the dotstructure of FIGURE 2, but the on-off tone is completely suppressedduring the production of the variable width furrows 24. Thus, the scancycle is made up of a sequence of four conditions, rather than two, inregions of highlight tone production:

(1) A line of dots with the screen tone on, phased zero degrees.

(2) A line engraving with the screen tone off.

(3) A line of dots with the screen tone on, but phased 180 degrees.

(4) A line engraving with the screen tone off.

Since the furrow width, from point to point along its direction, willhave to be controlled independently from the penetration of the styluswhen making a purely dot pattern, alternate control channels areprovided to produce the desired output signals for the control of stylusduring successive lines of engraving, as will be described.

In FIGURE 3, an alternate to the technique of FIG- URE 2 is pictured. Inthis case, the hill-and-dale auxiliary line is replaced by a line ofdots formed with the stylus operating at double the frequency of theprimary engraving frequency. This technique has the advantage over thehill-and-dale system in that it can engrave to a greater depth where theconnectors are being removed, and thereby reduce the elevation of theremaining connector to a greater degree. This is desirable in that, iftoo great a pressure is used in the printing process, ink is notdeposited on the shallow connectors and thereby printed. The scan cyclefor producing the plate asv depicted in FIGURE 3 would occur in thefollowing sequence:

(1) A line of dots with the single frequency tone on, phased zerodegrees.

(2) A line of double frequency dots with a phase shift of 90 degrees.

(3) A line of single frequency dots with the screen tone on, but phased180 degrees with respect to the first line of single frequency dots,

(4) A line of double frequency dots with phasing at 90 degrees to theprevious line of single frequency dots.

It has been found that plates engraved with this double frequencytechnique, when sterotyped by the newspaper process referred to asmatting, produce much better reproductions than the dot structure formedby the hill-anddale technique first described.

Experience with the cold-engraved patterns made according to theinvention demonstrates that while the highlight dot is not perfectlysquare, it does correspond closely to a rectangular shape, occasionallysomewhat elongated in the direction of scan, and with a slight dimple ineach edge as indicated at 28 in FIGURE 2. However, it has been foundpossible to produce an effective dot size (at the printing surface) assmall as 0.001 inch on the side. Moreover, the presence of theconnectors or grid lines 22 in the middle tone region has been founddistinctly advantageous, since their presence eliminates the so-calledhalf-tone break between shadow and middle tone regions. Furthermore, thefact that the stylus penetration is never so great as to permit anoverlap of the excised cavities, permits faster operation of the stylusin its reciprocating motion, and in turn permits either a fasterengraving action or the production of steeper-walled cavities, both ofwhich are desirable features.

It will be apparent to those skilled in this art that the provision of asingle machine for carrying out the foregoing procedures will also makeit readily possible to produce line engravings as such, by simplechanges in the line advance rate and complete suppression of the on-olfor screen tone. Thus, a machine can be produced which will be capable ofconventional hot-burning, cold half-tone engraving, or direct line work.

FIGURE 4 of the drawings shows schematically one form of apparatus bywhich the novel methods may readily be practiced. The mechanical partsof the equipment are quite similar to the machine of the Boyajeanreissue patent, including a drive motor 30 and gearing by which arerotated the cylinder 32 for carrying an original continuous tone imagesuch as a news photo or the like and the cylinder 34 for carrying theplate to be engraved with a half-tone reproduction of the image. Ascanner carriage 36 carries the usual focussed spot light source 38 landthe photocell pickup 40, while an engraver carriage 42 supports theusual stylus drive motor 44 operative to drive the stylus 46 toward andaway from the plate surface for dot production. The two carriages areconnected for concurrent axial motion (parallelto the axes of thecylinders) by a drive connection 48 from the same motor power source.Suitable guides, bearings and the like have been omitted from thedrawing in the interest of simplification of the illustration. Afixed-frequency tone-wheel 50, as described in the reissue patent, or ofother known type, provides the screen signal synchronized with cylinderrotation.

In the case of double frequency engraving, the double frequency signalis readily obtained by clipping the single frequency screen signal,differentiating it, amplifying, clipping, and then wave shaping. The 90degree phase shift is obtained by well-known techniques.

Various switching arrangements may be employed to produce the desireddot-position stagger as between successive rows of engraved dots, thearrangement illustrated including a dot or tone frequency amplifier andphase inverter 52 providing outputs which are 180 degrees apart in phaseposition with respect to cylinder rotation, and a relay 54 is energizedand de-energized, during successive groups of two complete rotations ofthe cylinders, to

apply the screen tone in desired stagger phase to the amplifier, clipperand ,wave shaper 56. A relay 58 controls contacts 59 to permit the toneoutput to be interruped entirely, during the second revolution of eachsuch group of two revolutions, to prevent the screen tone frommodulating the image signal during those revolutions in which, becauseof the existence of a highlight region under scanner cell 40, a simplehill-and-dale or varying Width cut is to be made.

The signals derived from scanner cell 40 are amplified by a preamplifier60, and during alternate single revolutions of the cylinders, areapplied to alternate compensating amplifier networks 62 and 64 forindependent regulation of the functional relation between the inputsignal and the desired depth of penetration of the stylus 46 into thematerial of the engraved plate on cylinder 34. This switching isaccomplished by contacts 66 operated by a relay 68, and the outputs ofthe two com: pensating channels are likewise synchronously switched asby another contact set 70 of the same relay 68. The respective signalsare then conveyed to the balance amplifier 72 which provides a separateand independent level control for the dot and hill-and-dale operations,as by respective potentiometers 74 and 76.

In view of the fact that the screen tone is interrupted during thehill-and-dale or variable width cut, the alternate switching of theouput of balance amplifier 72 can readily be accomplished by a secondset of contacts 78 of relay 58.

From the description above regarding the four different conditions whichwill exist during the engraving of a highlight reproduction, it willhave been realized that the change in phase of the screen tone appliedas a modulation to the amplified output signal in final mixer amplifier80 must take place only at the completion of two complete rotations ofthe cylinders, while the shift as between dot engraving and furrowengraving, when it happens, must occur after each single revolution.This can easily be provided in a number of obvious ways, including theuse of two-to-one counter, or by use of stick or latchtype relayssuitably triggered and released once every one or two revolutions.FIGURE 4 illustrates an arrangement in which the shaft of the cylindersdrives the smaller gear of a two-to-one gear set 82, there being ahalf-circular cam 84 on the larger gear, arranged to close contacts 86during each alternate rotation of the cylinders, and open them duringthe intervening rotations. Additionally, the large gear of set 82 drivesthe small gear of a second twoto-one gear set 88, whose larger gear alsocarries a halfcircular cam 90 engaging switch contacts 92 to close themduring two rotations of the cylinders, and to open them during the nexttwo revolutions. Closure of contacts 86 energizes relay 68 as alreadydescribed to accomplish the desired transfer as between dot engravingand hill-and-dale during alternate successive revolutions of thecylinders, at contacts 66 and 77, and also, over a branch conductor 94,energizes relay 58 to switch the output of amplifier 72 and to cut thetone modulation on or off at contacts 78 and 59.

During the next group of two cylinder revolutions, exactly the samesequence occurs, but in this case the phase position of the screen tonewill be reversed degrees by the energization of relay 54 over conductor96 from contacts 92. Thus, during the production of two successiveengraved lines of dots, the desired stagger of position will result,while the intervening lines of furrow-production, when called for by thehighlight signals from scanner cell 40 (as modified by thecharacteristics of the compensating amplifiers 62 and 64 and the balanceamplifier 72), will be obtained in the desired manner. The amplifiercharacteristics are so chosen, as will be understood, that in no casewill the engraved dot-forming cavities actually overlap, or even quitetouch one another at their corners; this condition can be insured by theuse of suit- 7 able and well-known signal shaping techniques, asindicated for the amplifiers 62 and 64.

From the method standpoint, it is clear that an equivalent engravedplate could be obtained by the use of two complete scans, all of the dotpattern and waffleiron grid of FIGURE 2 or FIGURE 3 being engravedduring one scan, and all of the furrow production or double-frequencyengraving being obtained as a second operation. However, there aremanifest technical advantages in the single-operation procedureoutlined, for example in reduction of the need for careful positioningof the stylus at the beginning of the second complete scan operation.Theoretically, at least, the furrowing or double-frequency operationcould even be performed as a first operation, followed by the half-tonedot production, and it is at least conceivable that a skillfull operatorcould produce a printable plate by hand engraving according to thepatterns suggested herein.

A further advantage in the line-by-line interchange of the dot andfurrow (or dot and double-frequency dot) functions across the platewidth is that it enables the operator to obtain a complete appraisal ofthe progress of the Work after each line or pair of lines, for exampleby the use of the stroboscopic microscope described in the Boyajeanpatent.

While the invention has been disclosed herein in connection with apreferred procedure and apparatus, it should be understood that giventhe novel concept, those skilled in the art will be able to implementthe same by other forms of apparatus and even by variant procedures toproduce the new form of plate, and that the invention is not to beconsidered as restricted to the details given above, except as may berequired by the scope of the appended claims.

What is claimed is:

1. A half-tone printing plate having an engraved pattern ofsubstantially rectangular outline cavities having their boundary linesoriented at degrees to the plate edges throughout its shadow and middletone regions, and in its highlight regions a pattern of such cavitiesfrom whose boundaries at least a part of the inter-cavity connectingmaterial is absent along lines parallel to one edge only of said plate,to provide highlight dots at the printing surface which are centered onthe center-lines of said cavities that are parallel to the plate edges.

2. A half-tone printing plate having an engraved pattern of spacedaligned cavities whose outlines throughout its shadow and middle toneregions are substantially rectangular figures in the printing plane ofthe plate, with their edges inclined at 45 degree angles to the edges ofthe plate, to provide in the middle tone regions continuouscavity-bounding grid lines at the printing surface; Said plate in itshighlight regions having a pattern of isolated printing dotsconstituting the residual intersections of the grid line boundaries ofsuch middle-tone cavities.

3. A half-tone printing plate in accordance with claim 2, in which saidhighlight region printing dots are or cruciform outline.

References Cited by the Examiner UNITED STATES PATENTS 569,595 10/96Amstutz. 2,032,541 3/36 Losier 101401.1 2,047,851 7/36 Bennett.2,086,798 7/37 Greenberg. 2,768,577 10/ 56 Boyajean 101-401 DAVID KLEIN,Primary Examiner.

1. A HALF-TONE PRINTING PLATE HAVING AN ENGRAVED PATTERN OFSUBSTANTIALLY RECTANGUALR OUTLINE CAVITIES HAVING THEIR BOUNDARY LINESORIENTED AT 45 DEGREES TO THE PLATE EDGES THROUGHOUT ITS SHADOW ANDMIDDLE TONE REGIONS, AND IN ITS HIGHLIGHT REGIONS A PATTERN OF SUCHCAVITIES FROM WHOSE BOUNDARIES AT LEAST A PART OF THE INTER-CAVITYCONNECTING MATERIAL IS ABSENT ALONG LINES PARALLEL TO ONE EDGE ONLY OFSAID PLATE, TO PROVIDE HIGHLIGHT DOTS AT THE PRINTING SURFACE WHICH ARECENTERED ON THE CENTER-LINES OF SAID CAVITIES THAT ARE PARALLEL TO THEPLATE EDGES.